The present invention relates generally to air data sensing systems for use on aircraft. More particularly, the present invention relates to multi-function probes, air data systems and methods of achieving dissimilarity and independence of air data outputs.
Air data systems that calculate the aerodynamic aircraft angle of attack (AOA) and angle of sideslip (AOS) of an air vehicle utilizing independent probes that are not pneumatically coupled, but which have processors for interchanging electrical signals between the probes, are known in the art. These probes are sometimes referred to as electronic multi-function probes (MFPs) or air data sensing probes (ADSPs). One type of electronic MFP is the SmartProbe sold by Goodrich Corporation. Multi-function probes include processing circuitry located at the probe itself as part of its instrument package, and are therefore sometime referred to as electronic multifunction probe air data computers. During sideslip of the air vehicle, compensation of various local (to the probes) parameters or signals, such as angle of attack and static pressure, is necessary for accurate determination of aircraft angle of attack and other aircraft parameters including determination of altitude from static pressure or other means. This requirement for accuracy in altitude indications is particularly important in Reduced Vertical Separation Minimum (RVSM) space areas of the air traffic control system.
In conventional air data systems, probes on opposite sides of an aircraft can be pneumatically connected so that the pressure signals are averaged between the right side of the aircraft and the left side of the aircraft to provide a static pressure that is xe2x80x9cnearly truexe2x80x9d. In most conventional systems therefore, although corrections are made for Mach number and aircraft angle of attack, it is rare that neglecting sideslip effect will introduce enough error to warrant a correction based on sideslip for the cross coupled probes. However, electronic MFPs are connected only electrically in order to eliminate the need for pneumatic tubing passing between the opposite sides of the aircraft or between probes on the same side of the aircraft. This means that each probe is pneumatically independent, even if it is electrically communicating with other probes.
As aircraft systems such as flight control systems and stall protection systems become more highly integrated, complex and automated, the integrity of the air data information that is used by these aircraft systems becomes increasingly more critical. These highly complex systems require redundant inputs of air data information that are measured by independent sources. Furthermore, the independent sources of air data are desired to be derived from dissimilar equipment to reduce the risk of common mode errors occurring amongst the separate sources of air data. This independence and dissimilarity of air data outputs is strongly recommended by certification authorities in the United States and Europe. The dissimilarity and independence ensures a level of safety that is consistent with the complexity of the systems that are consuming the data.
As an example, in RVSM space areas of the air traffic control system, the United States Federal Aviation Administration (FAA) allows aircraft to fly with only 1,000 feet of vertical separation, but requires that the altimetry system must meet stringent accuracy requirements. Further, the FAA requires that an aircraft have at least two independent altimetry systems, preferably dissimilar systems. Further, dissimilarity in aircraft systems becomes even more important in fly-by-wire aircraft systems and operation. Because the aviation authorities consider the loss of air data systems as being catastrophic, they require that the probability of such a loss be extremely low. For example, a current requirement is that the probability of the air data system being lost be less than 10xe2x88x929. If two independent air data systems have the remote possibility of experiencing common mode failures, the authorities are likely to determine that the probability of a loss of all air data systems exceeds this threshold. An additional requirement enforced by the FAA and JAA is called out under FAR/JAR 25.1309, which states that xe2x80x9cno single failure may result in a catastrophic event.xe2x80x9d Thus, the assurance of eliminating common mode failures is paramount.
To provide redundancy in estimations of aircraft AOA and AOS, multiple electronic MFPs are used in an air data sensing system. The multiple electronic MFPs can be used in pairs to define multiple probe systems each having two electronic MFPs as members. A single electronic MFP can be a member of several different probe systems. It is known that estimations of local AOA at two MFPs in a probe system can be used to predict aircraft AOA and aircraft AOS. It is also know that aircraft AOA and AOS can be calculated or estimated by using the local pressure ratios Psl/qcl, where Psl is the local static pressure and qcl is the local impact pressure (the difference between the total pressure and the local static pressure, PTxe2x88x92Psl) from each of two uniquely located probes. In other words, each two-probe system can arrive at estimations of aircraft AOA and aircraft AOS which are a unique function of the local AOA estimations at the two probes or a unique function of the pressure ratio Psl/qcl at each probe.
One advantage of utilizing electronic multifunction probe air data computers in air data applications is the use of common equipment for all probes, thereby reducing the number of line replaceable unit (LRU) spares required for the aircraft. The disadvantage of this commonality is that, traditionally, there exists no dissimilarity between the electronic multifunction probe systems. The lack of dissimilarity exposes the air data system to the risk of common mode failures in hardware, firmware and software thereby potentially comprising the integrity of the system.
Consequently, systems and methods for realizing dissimilar and independent air data output would be a significant improvement in the art.
A system for providing independent and dissimilar aircraft parameter estimations includes first and second dual-channel electronic multi-function probes (MFPs) positionable adjacent an aircraft skin. Each dual-channel electronic MFP has pressure sensing ports and an electronics housing. Located within the electronics housing of each dual-channel electronic MFP are first and second electronics channels. The first electronics channel of the first dual-channel electronic MFP is electrically coupled with the first electronics channel of the second dual-channel electronic MFP to provide a first air data system providing aircraft parameter estimations. The second electronics channel of the first dual-channel electronic MFP is electrically coupled with the second electronics channel of the second dual-channel electronic MFP to provide a second air data system providing aircraft parameter estimations. The first and second air data systems are independent and dissimilar from one another.